The formulation of lubricants typically includes an additive package incorporating a variety of chemicals to improve or protect lubricant properties in application specific situations, particularly internal combustion engine and machinery applications. The more commonly used additives include oxidation inhibitors, rust inhibitors, antiwear agents, pour point depressants, detergent-dispersants, viscosity index (VI) improvers, foam inhibitors and the like. This aspect of the lubricant arts is specifically described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pp477-526, incorporated herein by reference. Considering the diversity of chemical structures represented by the plethora of additives incorporated in a typical lubricant formulation, and the quantity in which they are added, the artisan in the lubricant formulation arts faces a substantial challenge to provide a homogeneous formulation which will remain stable or in solution during inventory and during use. Lubricants, particularly synthetic lubricants of the type of interest in the instant invention, can be hydrogenated olefins. Due to their relatively non-polar hydrocarbon structure they are often incompatible with polar additives such as antioxidants, antirust and antiwear agents, etc. Accordingly, in order to render the lubricants compatible with the polar additives large amounts of expensive polar organic esters must be added to the formulation. Useful commercial formulations may contain 20% percent or more of such esters as bis-tridecanol adipate for example, solely to provide a fully homogeneous lubricant blend of lubricant and additive.
Modifying the solvent properties of lubricants with solubilizing agents such as organic esters, while solving the problem of how to prepare stable blends with lubricant additives, creates or accentuates other performance related problems beyond the added burden on cost of the product. Performance problems can include volatility, thermal stability, oxidative stability and the like. Accordingly, workers in the field are challenged by the need to incorporate the desirable properties of additives into lubricants, without incurring the usual physical performance and cost liabilities.
One class of lubricants of particular interest in the present invention are synthetic lubricants obtained by the oligomerization of olefins, particularly C.sub.6 -C.sub.20 alpha olefins. Catalytic oligomerization of olefins has been studied extensively. Many catalysts useful in this area have been described, especially coordination catalyst and Lewis acid catalysts. Known olefin oligomerization catalysts include the Ziegler-Natta type catalysts and promoted catalysts such as BF3 or A1C13 catalysts. U.S. Pat. No. 4,613,712 , for example, teaches the preparation of isotactic alpha-olefins in the presence of a Ziegler type catalyst. Other coordination catalysts, especially chromium on a silica support, are described by Weiss et al in Jour. Catalysis 88, 424-430 (1984) and in Offen. DE 3,427,319.
Poly alpha-olefin (PAO) oligomers as reported in literature or used in existing lube base stocks are usually produced by Lewis acid catalysis in which double bond isomerization of the starting alpha-olefin occurs easily. As a result, the olefin oligomers have more short side branches and internal olefin bonds. These side branches significantly degrade their lubricating properties. Recently, a class of synthetic, oligomeric, polyalpha-olefin lubricants, referred to herein as HVI-PAO, has been discovered, as reported in U.S. patent application Ser. No. 946,226 filed Dec. 24, 1986 now abandoned, with a regular head-to-tail structure and containing a terminal olefinic bond. The HVI-PAO oligomers are produced by the oligomerization of C.sub.6 -C.sub.20 1 -alkene in contact silica supported chromium oxide catalyst which has been reduced to a lower valence state. These unsaturated lubricants have shown remarkably high viscosity index (VI) accompanied by surprising low pour points and are especially characterized by having a low branch ratio of methyl to methylene groups, as defined hereinafter. While these favorable properties can be further improved by the use of lubricant additives usually containing polar functionality to confer antiwear, anticorrosive, etc. attributes on the novel lubricant, they cannot be so improved without incurring the aforementioned problems associated with the addition of additives.
Accordingly, it is an objective of the instant invention to enhance the properties of HVI-PAO by incorporating additive functional groups into the lubricant molecular structure.
It is an objective of the instant invention to provide improved lubricant or fuel compositions having superior wear and anticorrosive characteristics by epoxidizing the olefinic bond of HVI-PAO.
Yet another objective of the present invention is to provide blends of epoxidized HVI-PAO with other lubricants yielding mixtures with improved properties and lower cost.
A further object of the invention disclosed herein is to provide superior lubricants by incorporating performance-enhancing additives into epoxidized HVI-PAO as a mixture therein.